Pentode (EF86) pre-amps and combo's?

[DaveW]

I came across this link about the little dot headphone amp which uses the 5725 as a preamp tube, so I guess they must be OK for audio applications.

http://www.littledot.net/forum/viewtopic.php?f=9&t=815" onclick="window.open(this.href);return false;

[jazbo8]

I came across this link about the little dot headphone amp which uses the 5725 as a preamp tube, so I guess they must be OK for audio applications.

http://www.littledot.net/forum/viewtopic.php?f=9&t=815" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

Found a brief mention on AX84, a few more others to try as well.

[StarGeezers]

Lots of pentode Fun going on at Wattkins ... http://www.wattkins.com/node/18704" onclick="window.open(this.href);return false;

[Isaac Stuckey]

Lots of people talk about pentode problems in preamp and microphonics, but can anyone advise on building a ef86 preamp (ac15 amp actually), into a head. Many of the posts I have read are in regard to noise problems from speakers etc. but I'm building a head, so any ideas?

[Freddy]

You will have less microphonic tube problems with a head style amp build. The speaker will not be beating the snot out of the tiny little innards in those tubes so the ones that start out not microphonic will usually stay that way. One downside is you will need two hands instead of one to transport the amp. There used to be a couple of 18 watt layouts with an EF86 in the download section. No Vox layouts though.

[Isaac Stuckey]

It'll only weigh maybe 18-20lbs, but do you mean two hands for stability, or they don't like shaking, or what? I assumed it would be better in a head, as I have read a bunch of the posts here on ef86's, and everyone seems to build them into combos and they get insanely beat up by speakers. I have a AC30/4 schematic I'm using. And I searched the AC15 schematic several times on the internet, they are so close it was fine.
Thanks,

[Daviedawg]

Maybe he means a speaker cab in one hand and head in the other?

Dd

[CurtissRobin]

+1
When you set up the head at a gig or a session, be sure to put it on something that doesn't vibrate (i.e. on or in front of a speaker cab) or get bumped around. Set it on top of a layer or two of padding on a chair or a small parsons table (I love my $7.99 Ikea "Lack" table for my home rig) or atop an effects rack. The pad attenuates and damps vibration and the "remote" location avoids vibration due to direct contact.

BTW the leg spacing of that Ikea "Lack" table http://www.ikea.com/us/en/catalog/products/20011413/" onclick="window.open(this.href);return false; is just right for a poor man's rack. 19" rack equipment fits nicely and you can use sheet metal screws to mount things (just be sure to pilot drill the holes in the legs so they don't crumble when you drive the screws).

KennyO

[JMPGuitars]

If you're worried about vibration, you could probably also use speaker isolation foam, like the stuff they use under studio monitors.

[Freddy]

I did mean amp head in one hand and speaker cabinet in the other. Usually means one more trip back to the car to get the guitar. A lot of times those microphonic tubesthat rattled and howled in a combo work fine in a head in the v2 or v3 spot.

[rexracer]

I think you also get better tone out of a dedicated tone cabinet, combo cabs are just for convenience imho.

[Isaac Stuckey]

Finished mine yesterday. Sounds great, except need to reduce the el84 cathode cap from 18watt value (500uf) to 250uf like in a ac15, and a couple small tweaks, but it sound great, maybe the fact that I used original Celestion Blue (Vox Silver Bulldogs) speakers for playing, in a 2x12 cab... Guess that helps, but sound really great though.
Anyway, Yea in a head cabinet it sounds pretty good. I had to take the tube shield off of it as it rattled, and it really only is as Microphonic as a bad 12ax7, so its pretty reasonable. And no problems with it right on top of the cabinet. I played it through a little 1x12 with a WGS reaper in it and that was great too. It squeals with my tele, when you dime it, so I gotta try some other guitars too, as It's just that that guitar is a little microphonic itself, as the pickups arent potted. but they are pretty good.

[tubenit]

The 5879 pentode is a nice alternative to the EF86. We've used this in V1 in numerous builds including the HoSo56 which originally had EL84's.

http://www.el34world.com/Forum/index.php?topic=6176.0" onclick="window.open(this.href);return false;

and in overdrive sections of amps like this one:

http://www.el34world.com/Forum/index.php?topic=9636.0" onclick="window.open(this.href);return false;

With respect, Tubenit

[katopan]

I've got the AC15 EF86 preamp as a second channel in my 18 Watt head. Works fine except for the EF86 in there at the moment has gone noisy (it crackles) and needs replacing. I've never had microphonic issues with it.

[Ingo]

Hello

another very good option is to use a used EF804 from Telefunken. The differences to the EF86 are very small and it is a really very stable tube with less micro phonics than the today available 12AX7A, even selected. I have build some custom amps with that tube and the sound is really wonderful.

Best regards
Ingo

[Isaac Stuckey]

Tubenit,
That tweed OD special schematic looks really interesting, I liked the tone, slightly interested in building one now. That would be cool.

Also, Ingo, You mentioned the EF804, is that a direct replacement for the EF86 pinwise? Does it have the same gain properties? Like would it be less gain kind of like the difference between a 12ax7 and a 12ay7 or is it similar?

[CurtissRobin]

I looked for the EF804 and found that it's a tube the sellers are very proud of. i.e. $$.

KennyO

[JMPGuitars]

I use EF806S which is a direct replacement for EF86 and they sound fantastic.

[Isaac Stuckey]

The EF806s isn't too cheap either, but definitely would be nice to experiment a little further. I'm hoping to build another AC15 soon, so when I get another EF86, I'll have to try another variant or two...

[AC Cobra]

I got a new tung-sol ef806, so Ill see what that will do in a head. A little off topic, bit somewhat realivant... dose anyone know of a good way to tone controll schematic? I was thinking of the matchless/orange style rotary tone controll, although with the right coupling cap I would be happy no tone controlls. Just gain and volume.
I will be using mearlins values for the ef86 section, which Im sure Ive seen zaphood refrence at one point